ReRAM structure and method of fabricating the same

ABSTRACT

An ReRAM structure includes a dielectric layer. A first ReRAM and a second ReRAM are disposed on the dielectric layer. The second ReRAM is at one side of the first ReRAM. A trench is disposed in the dielectric layer between the first ReRAM and the second ReRAM. The first ReRAM includes a bottom electrode, a variable resistive layer and a top electrode. The variable resistive layer is between the bottom electrode and the top electrode. A width of the bottom electrode is smaller than a width of the top electrode. The width of the bottom electrode is smaller than a width of the variable resistive layer.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a resistive random access memory (ReRAM) structure and a method of fabricating the same, and more particularly to an ReRAM structure which can prevent current leakage and a method of fabricating the same.

2. Description of the Prior Art

Nonvolatile memory is capable of retaining the stored information even when unpowered. Non-volatile memory may be used for secondary storage or long-term persistent storage. Resistive Random Access Memory (ReRAM) technology has been gradually recognized as having exhibited those semiconductor memory advantages.

ReRAM cells are non-volatile memory cells that store information by changes in electric resistance, not by changes in charge capacity. In general, the resistance of the resistive layer varies according to an applied voltage. An ReRAM cell can be in a plurality of states in which the electric resistances are different. Each different state may represent a digital information. The state can be changed by applying a predetermined voltage or current between the electrodes. A state is maintained as long as a predetermined operation is not performed.

However, the manufacturing process of the ReRAM often causes current leakage.

SUMMARY OF THE INVENTION

In light of the above, the present invention provides a structure and a method to prevent the current leakage of an ReRAM.

According to a preferred embodiment of the present invention, an ReRAM structure includes a dielectric layer. A first ReRAM is disposed on the dielectric layer. The first ReRAM includes a bottom electrode, a top electrode, and a variable resistive layer disposed between the top electrode and the bottom electrode. A width of the bottom electrode is smaller than a width of the top electrode. The width of the bottom electrode is smaller than a width of the variable resistive layer. A second ReRAM is disposed on the dielectric layer and at one side of the first ReRAM. A trench is disposed in the dielectric layer between the first ReRAM and the second ReRAM.

According to a preferred embodiment of the present invention, a fabricating method of an ReRAM structure includes providing a dielectric layer. Then, a mask layer is formed to cover the dielectric layer. Part of the mask layer is removed to form a first recess and a second recess within the mask layer. Later, a first bottom electrode and a second bottom electrode are formed, wherein the first bottom electrode is disposed in the first recess, and the second bottom electrode is disposed in the second recess. Subsequently, a trench is formed in the mask layer between the first bottom electrode and the second bottom electrode and in the dielectric layer. Next, a variable resistive material layer and a top electrode material layer are formed in sequence to cover the mask layer, the first bottom electrode and the second bottom electrode, wherein the variable resistive material layer covering the first bottom electrode serves as a first variable resistive layer, the top electrode material layer covering the first bottom electrode serves as a first top electrode, a width of the first bottom electrode is smaller than a width of the first top electrode, and the width of the first bottom electrode is smaller than a width of the first variable resistive layer. Finally, a protective layer is formed to cover and contact the top electrode material layer and a sidewall of the trench.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 to FIG. 8 depict an ReRAM structure and a method of fabricating an ReRAM structure according to a preferred embodiment of the present invention, wherein:

FIG. 1 depicts a dielectric layer covered by a mask layer;

FIG. 2 depicts a stage following FIG. 1;

FIG. 3 depicts a stage following FIG. 2;

FIG. 4 depicts a stage following FIG. 3;

FIG. 5 depicts a stage following FIG. 4;

FIG. 6 depicts a stage following FIG. 5;

FIG. 7 depicts a stage following FIG. 6; and

FIG. 8 depicts a stage following FIG. 7.

FIG. 9 depicts an ReRAM structure according to a preferred embodiment of the present invention.

FIG. 10 depicts a top view of a first ReRAM, a second ReRAM and a trench.

DETAILED DESCRIPTION

FIG. 1 to FIG. 8 depict an ReRAM structure and a method of fabricating an ReRAM structure according to a preferred embodiment of the present invention.

As shown in FIG. 1, a dielectric layer 10 is provided. A metal interconnection 12 such as a contact plug 12 a and a contact plug 12 b is disposed within the dielectric layer 10. The dielectric layer 10 can be silicon oxide, silicon nitride, silicon carbon nitride, silicon oxynitride or silicon oxycarbonitride. Next, a mask layer 14 is formed to cover the dielectric layer 10. The mask layer 14 may be silicon nitride. The metal interconnection 12 can be copper, aluminum, tungsten or other conductive materials.

As shown in FIG. 2, the mask layer 14 is patterned to remove part of the mask layer 14 and to form a first recess 16 a and a second recess 16 b in the mask layer 14. The first recess 16 a and the second recess 16 b penetrate the mask layer 14. Moreover, the contact plug 12 a is exposed through the first recess 16 a, and the contact plug 12 b is exposed through the second recess 16 b. As shown in FIG. 3, a bottom electrode material layer 22 is formed to cover the mask layer 14 and fill up the first recess 16 a and the second recess 16 b. The bottom electrode material layer 22 includes titanium nitride, tantalum nitride or other conductive materials. The method of forming the bottom electrode material layer 22 is preferably through a physical deposition process.

As shown in FIG. 4, a planarization process 20 such as a chemical mechanical polish is performed to remove the bottom electrode material layer 22 outside of the first recess 12 a and the second recess 12 b. The bottom electrode material layer 22 remained in the first recess 12 a serves as a first bottom electrode 22 a. The bottom electrode material layer 22 remained in the second recess 12 b serves as a second bottom electrode 22 b. The first bottom electrode 22 a contacts the contact plug 12 a. The second bottom electrode 22 b contact the contact plug 12 b.

As shown in FIG. 5, a trench 24 is formed in the mask layer 14 between the first bottom electrode 22 a and the second bottom electrode 22 b and in the dielectric layer 10 (please refer to FIG. 10 for the relative positions of the trench 24, the first bottom electrode 22 a and the second bottom electrode 22 b with respective to a top view). The trench 24 is formed by an anisotropic etching process 26 such as a dry etching process. A sidewall of the trench 24 is vertical. In other words, the sidewall of the trench 24 is flat. As shown in FIG. 6, an isotropic etching process 28 is performed to the trench 24. The isotropic etching process 28 may be a wet etching process. After the isotropic etching process 28, the sidewall of the trench 24 turns into an arc 30 and the bottom of the trench 24 becomes deeper. The arc 30 bends into the dielectric layer 10. According to a preferred embodiment of the present invention, an aspect ratio of the trench 24 is larger than 1.76.

As shown in FIG. 7, a variable resistive material layer 32 is formed to cover the mask layer 14, the first bottom electrode 22 a, the bottom of the trench 24 and the second bottom electrode 22 b. Later, a top electrode material layer 34 is formed to cover the variable resistive material layer 32. The variable resistive material layer 32 and the top electrode material layer 34 are both formed by physical vapor depositions. The top electrode material layer 34 includes titanium nitride or tantalum nitride, and the variable resistive material layer 32 includes tantalum oxide, hafnium oxide or titanium oxide. A total thickness of the top electrode material layer 34 and the variable resistive material layer 32 is between 500 and 1000 angstroms. It is noteworthy that the present invention specially forms the trench 24 and uses the physical vapor deposition to form the variable resistive material layer 32 and the top electrode material layer 34. Furthermore, the aspect ratio of the trench 24 goes along with the total thickness of the variable resistive material layer 32 and the top electrode material layer 34 to make the variable resistive material layer 32 and the top electrode material layer 34 to form an overhang on the sidewall of the trench 24. Furthermore, the arc 30 formed by the isotropic etching process 28 bends into the dielectric layer 10. Because the trench 24 has the arc 30 and a proper aspect ratio, the variable resistive material layer 32 and the top electrode material layer 34 can't form connective structure on the sidewall of the trench 24. The variable resistive material layer 32 and the top electrode material layer 34 can only be deposited on part of the trench 24 and the bottom of the trench 24. In some cases, the variable resistive material layer 32 and the top electrode material layer 34 can't be deposited on the sidewall of the trench 24. In this way, the variable resistive material layer 32 and the top electrode material layer 34 are separated into three regions to respectively cover the first bottom electrode 22 a, the bottom of the trench 24 and the second bottom electrode 22 b. In detail, the variable resistive material layer 32 covers the first bottom electrode 22 a serves as a first variable resistive layer 32 a. The top electrode material layer 34 covers the first bottom electrode 22 a serves as a first top electrode 34 a. The variable resistive material layer 32 covers the second bottom electrode 22 b serves as a second variable resistive layer 32 b. The top electrode material layer 34 covers the second bottom electrode 22 b serves as a second top electrode 34 b. At this point, the first bottom electrode 22 a, the first variable resistive layer 32 a and the first top electrode 34 a form a first ReRAM 100 a. The second bottom electrode 22 b, the second variable resistive layer 32 b and the second top electrode 34 b form a second ReRAM 100 b. Moreover, a width W1 of the first bottom electrode 22 a is smaller than a width W3 of the first top electrode 34 a. The width W1 of the first bottom electrode 22 a is smaller than a width W2 of the first variable resistive layer 32 a. Similarly, a width W4 of the second bottom electrode 22 b is smaller than a width W6 of the second top electrode 34 b, and the width W4 of the second bottom electrode 22 b is smaller than a width W5 of the second variable resistive layer 32 b. In addition, the first variable resistive layer 32 a and the second variable resistive layer 32 b both contact the mask layer 14.

As shown in FIG. 8, a protective layer 36 is formed to cover and contact the top electrode material layer 34 and the sidewall of the trench 24. The protective layer 36 is preferably formed by a chemical vapor deposition. The protective layer 36 directly contacts the sidewall of the trench 24 which is not covered by the variable resistive material layer 32 and the top electrode material layer 34. Therefore, the protective layer 36 electrically isolates the first ReRAM 100 a, the second ReRAM 100 b, the variable resistive material layer 32 and the top electrode material layer 34 from each other. The protective layer 36 can be silicon nitride, silicon oxide, silicon oxynitride, silicon carbon nitride or other insulating materials.

As shown in FIG. 9, a dielectric layer 38 is formed to cover the protective layer 36. Then, a metal interconnection 40 is formed in the dielectric layer 38. The metal interconnection includes a contact plug 40 a and a contact plug 40 b. The contact plug 40 a contacts and electrical connects to the first top electrode 34 a. The contact plug 40 b contacts and electrical connects to the second top electrode 34 b. The metal interconnection 40 may be copper, aluminum, tungsten or other conductive materials. Furthermore, the first ReRAM 100 a and the second ReRAM 100 b can couple to the transistor 42 through the metal interconnection 12. However, the first ReRAM 100 a and the second ReRAM 100 b can be electrically connected to each other in other ways, not limited to the method mentioned above.

FIG. 9 depicts an ReRAM structure according to a preferred embodiment of the present invention. FIG. 10 depicts a top view of a first ReRAM, a second ReRAM and a trench.

Please refer to FIG. 9 and FIG. 10. A substrate 1 is provided. A transistor 42 is disposed on the substrate 1. The dielectric layer 10 covers the substrate 1. A metal interconnection 12 is disposed in the dielectric layer 10. A trench 24 is embedded in the dielectric layer 10 between the first ReRAM 100 a and the second ReRAM 100 b. The first ReRAM 100 a includes a first bottom electrode 22 a, a first top electrode 34 a and a first variable resistive layer 32 a. The first variable resistive layer 32 a is between the first bottom electrode 22 a and the first top electrode 34 a. Please also refer to FIG. 7. The width W1 of the first bottom electrode 22 a is smaller than the width W3 of the first top electrode 34 a. The width W1 of the first bottom electrode 22 a is smaller than the width W2 of the first variable resistive layer 32 a. The second ReRAM 100 b includes a second bottom electrode 22 b, a second top electrode 34 b and a second variable resistive layer 32 b. The second variable resistive layer 32 b is between the second bottom electrode 22 b and the second top electrode 34 b. The width W4 of the second bottom electrode 22 b is smaller than the width W6 of the second top electrode 34 b, and the width W4 of the second bottom electrode 22 b is smaller than the width W5 of the second variable resistive layer 32 b.

Moreover, a mask layer 14 contacts the dielectric layer 10 and is disposed at two sides of the first bottom electrode 22 a and two sides of the second bottom electrode 22 b. The top surface of the first bottom electrode 22 a, the top surface of the second bottom electrode 22 b and the top surface of the mask layer 14 are aligned with each other. As shown in FIG. 10, part of the first top electrode 34 a overlaps the trench 24. But, the first bottom electrode 22 a does not overlap the trench 24. Likewise, the part of the second top electrode 34 b overlaps the trench 24. But, the second bottom electrode 22 b does not overlap the trench 24.

A variable resistive material layer 32 covers a bottom of the trench 24, wherein a material of the variable resistive material layer 32 and a material of the first variable resistive layer 32 a and a material of the second variable resistive layer 32 b are the same. A top electrode material layer 34 covers the variable resistive material layer 32, wherein a material of the top electrode material layer 34 and a material of the first top electrode 34 a and a material of the second top electrode 34 b are the same. It is noteworthy that the variable resistive material layer 32, the first variable resistive layer 32 a, and the second variable resistive layer 32 b do not connect to each other. The top electrode material layer 34, the first top electrode 34 a, and the second top electrode 34 b do not connect to each other.

Moreover, part of the sidewall of the trench 24 is not covered by the variable resistive material layer 32. Similarly, part of the sidewall of the trench 24 is not covered by the top electrode material layer 34. A protective layer 36 covers the first ReRAM 100 a and the second ReRAM 100 b and contacts the sidewall of the trench 24 which is not covered by the variable resistive material layer 32. The sidewall of the trench 24 is in a shape of an arc 30. The arc 30 bends into the dielectric layer 10. The aspect ratio of the trench 24 is greater than 1.76. The total thickness of the first top electrode 34 a and the first variable resistive layer 32 a is between 500 and 1000 angstroms. The total thickness of the second top electrode 34 b and the second variable resistive layer 32 b is between 500 and 1000 angstroms. The first bottom electrode 22 a and the second bottom electrode 22 b respectively include titanium nitride or tantalum nitride. The first top electrode 34 a and the second top electrode 34 b respectively include titanium nitride or tantalum nitride. The first variable resistive layer 32 a and the second variable resistive layer 32 b respectively include tantalum oxide, hafnium oxide or titanium oxide. The protective layer 36 may be silicon nitride, silicon oxide, silicon oxynitride, silicon carbon nitride or other insulating materials.

A metal interconnection 40 includes a contact plug 40 a and a contact plug 40 b. The contact plug 40 a contacts and electrical connects to the first top electrode 34 a. The contact plug 40 b contacts and electrical connects to the second top electrode 34 b. The contact plug 12 a of the metal interconnection 12 contacts and electrical connects to the first bottom electrode 22 a. The contact plug 12 b of the metal interconnection 12 contacts and electrical connects to the second bottom electrode 22 b.

The conventional process fabricates ReRAM by depositing the bottom electrode material layer, the variable resistive layer, and the top electrode material layer in sequence. Later, the position of the ReRAM is defined by an etching process. However, the conventional process causes damages on the bottom electrode material layer, the variable resistive layer, and the top electrode material layer during the etching process. Then, the ReRAM formed by the conventional process will have a current leakage path between the top electrode and the bottom electrode. On the other hand, the present invention takes advantage of the physical vapor deposition having an overhang effect on the sidewall of the trench with a high aspect ratio to form the top electrode and the variable resistive layer without using any etching process. Furthermore, the bottom electrode of the present invention is formed by filling a conductive material layer into recesses followed by a planarization. Therefore, the formation of the bottom electrode of the present invention does not using any etching process. As a result, the current leakage can be prevented in the present invention.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims. 

What is claimed is:
 1. A resistive random access memory (ReRAM) structure, comprising: a dielectric layer; a first ReRAM disposed on the dielectric layer, wherein the first ReRAM comprises: a bottom electrode; a top electrode, wherein a width of the bottom electrode is smaller than a width of the top electrode; and a variable resistive layer disposed between the top electrode and the bottom electrode, wherein the width of the bottom electrode is smaller than a width of the variable resistive layer; a second ReRAM disposed on the dielectric layer and at one side of the first ReRAM; and a trench disposed in the dielectric layer between the first ReRAM and the second ReRAM; a variable resistive material layer covering a bottom of the trench, wherein a material of the variable resistive material layer and a material of the variable resistive layer are the same; and a top electrode material layer covering the variable resistive material layer, wherein a material of the top electrode material layer and a material of the top electrode are the same, and wherein the variable resistive material layer is entirely encapsulated by the top electrode material layer and the dielectric layer.
 2. The ReRAM structure of claim 1, wherein the variable resistive material layer does not connect to the variable resistive layer, and the top electrode material layer does not connect to the top electrode.
 3. The ReRAM structure of claim 1, wherein part of a sidewall of the trench is not covered by the variable resistive material layer, part of the sidewall of the trench is not covered by the top electrode material layer.
 4. The ReRAM structure of claim 1, wherein a sidewall of the trench is in a shape of a concave arc within the dielectric layer.
 5. The ReRAM structure of claim 1, further comprising a protective layer contacting and the covering the top electrode, a sidewall of the trench and the second ReRAM.
 6. The ReRAM structure of claim 1, wherein an aspect ratio of the trench is larger than 1.76, and a total thickness of the top electrode and the variable resistive layer is between 500 and 1000 angstroms.
 7. The ReRAM structure of claim 1, wherein the bottom electrode comprises titanium nitride or tantalum nitride, the top electrode comprises titanium nitride or tantalum nitride, and the variable resistive layer comprises tantalum oxide, hafnium oxide or titanium oxide.
 8. The ReRAM structure of claim 1, further comprising a mask layer disposed at two sides of the bottom electrode, and contacting a sidewall of the bottom electrode.
 9. The ReRAM structure of claim 1, further comprising a first metal interconnection contacting the bottom electrode and a second metal interconnection contacting the top electrode. 